Aerial vehicles often carry liquids either as fuel or as payload for delivery to one or more destinations. When such liquids are carried, for example for aerial spraying, transportation or mid-air refueling, there is danger of instability in the flight behaviour of the aerial vehicle on account of sloshing of the liquid during acceleration/deceleration or other sudden movements. To prevent such flight instability, it is necessary to implement “anti-sloshing” measures. The situation is particularly severe during low-altitude flights owing to greater turbulence owing to significant change in wind speed and direction in the first 30 meters of height over ground level caused by the varying frictional effect and undulations of the ground surface. Such low-level flights also require frequent flight course changes to avoid obstacles in the form of trees, bushes, and other structures, etc.
Conventional methods of implementing “anti-sloshing” include the incorporation of baffles and sub-compartments in the design of the container carrying the liquid. Such designs break large liquid surface areas into smaller surface areas and distribute resulting forces on greater container boundary surfaces to reduce the impact of sloshing. CN103935518A describes the use of such a combination of baffles on the inside and dampeners on outside of the container to reduce sloshing. However, there are three major drawbacks to these approaches:    (a) increased container weight, a parameter which is a premium on aerial platform,    (b) additional cost owing to increased material and design and construction complexity,    (c) sub-optimal performance owing to the use of a static structure which is designed for the worst-case scenario.
The anti-slosh performance of these solutions varies based on level of liquid inside the container, velocity profile of the aerial vehicle, etc.
Another known approach uses various types of float balls or energy-absorbers to reduce sloshing. US20150008235 describes an apparatus and method to limit slosh and spillage in a liquid container using such a technique. A plurality of balloons are disposed inside a liquid container to take up space as liquid is removed from the container. The balloons can be connected to a gas injection system to inject gas into the balloons ensure that the balloons fully occupy the empty space and maintain minimum exposed liquid surface area. This acts to limit the sloshing of the liquid inside the container. The balloons can be secured in place by one or more positioning boxes disposed along the inside periphery of the container. One or more strings can interconnect the balloons to the positioning boxes. However, the efficacy of this solution varies as fluid volume changes due to dispersion. Also, this approach requires additional components (balloons, strings, positioning boxes etc.) which increase the cost, weight, and design complexity.
The above-mentioned schemes do not monitor the sloshing behaviour and are unable to take any corrective action based on these observations. A research paper “Active Sloshing Control in a smart flexible cylindrical floating roof tank” by Hasheminejad et. al. focuses on the use of an exact 3-d coupled hydro-elastic model to analyse transient liquid sloshing in a vertically standing, flexible, circular cylindrical shell container fitted with a freely floating, piezo-sandwich, thin elastic circular plate. The sloshing is minimized by deploying two evolutionary heuristic optimization techniques to control the movement of the plate on the basis of measured volume displacement and volume velocity feedback of the sloshing liquid.
However, this design requires additional components (plate) which increases the cost, weight, and design complexity, and also suffers from poor performance in severe sloshing conditions and is susceptible to the potential for plate deformation etc. It is also restricted to a specific class of containers (vertically standing, flexible, circular cylindrical shell).
The present disclosure provides a solution which overcomes the above-stated limitations of the prior art by providing real-time control to maintain platform stability by counteracting and minimizing sloshing whenever necessary.